There is demand for high contrast ratios and high light utilization efficiencies in optical devices that control transmittance (or reflectivity) of incident light.
Liquid crystal panels are well known as optical devices that control light transmittance by applying voltage. Liquid crystal panels generally include a pair of substrates and a liquid crystal layer provided between the substrates. In liquid crystal panels, the alignment of the liquid crystal molecules varies according to the magnitude of the voltage applied to the liquid crystal layer, such that the transmittance of light incident on the liquid crystal panel changes. As liquid crystal panels can achieve substantially high contrast ratios, they are widely used as display devices.
However, as the majority of liquid crystal panels are of a type that utilizes a polarizing plate, more than half of the light used for the display is absorbed by the polarizing plate. As a result, the light utilization efficiency is low. Accordingly, in recent years, the development of optical devices that do not require polarizing plates is progressing.
In PTL 1, a display panel having a light modulation layer including a shape-anisotropic member is proposed. In the display panel of PTL 1, the shape-anisotropic member dispersed in the medium is rotated (that is, the alignment direction is changed) by application of an electrical field to the light modulation layer, such that the light transmittance (or light reflectance) of the light modulation layer is changed.
As the display panel of PTL 1 described above does not require a polarizing plate, its light utilization efficiency can be increased in comparison with liquid crystal panels.
In addition, PTL 2 proposes a light modulation panel capable of changing the direction of an electric field applied to a light modulation layer that includes a shape-anisotropic member. In this light modulation panel, the state in which a vertical electrical field is applied to the light modulation layer and the state in which a horizontal electrical field (or fringe electrical field) are applied to the light modulation layer are switched, such that display may be performed. The vertical electrical field is generated by a pair of solid electrodes opposing each other with the optical layer interposed therebetween, and the horizontal electrical field is generated by a pair of comb-tooth electrodes provided on one of a pair of substrates sandwiching the optical layer. In addition, the fringe electrical field is generated by the comb-tooth electrode and the solid electrode provided on one of the pair of substrates.